Simple function overloading in C

overload.c

#include <stdio.h>

/* Count variadic macro arguments (1-10 arguments, extend as needed)
 */
#define VA_NARGS_IMPL(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, N, ...) N
#define VA_NARGS(...) VA_NARGS_IMPL(__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

/* Simple name mangling of function sum based on arity
 */
#define __sum_impl2(n, ...) __sum_impl__ ## n(__VA_ARGS__)
#define __sum_impl(n, ...) __sum_impl2(n, __VA_ARGS__)
#define sum(...) __sum_impl(VA_NARGS(__VA_ARGS__), __VA_ARGS__)

int sum(int a, int b)
{
    return a + b;
}

int sum(int a, int b, int c)
{
    return a + b + c;
}

double sum(double a, double b, double c, double d)
{
    return a + b + c + d;
}

int main(void)
{
    printf("%d\n", sum(1, 2));
    printf("%d\n", sum(1, 2, 3));
    printf("%g\n", sum(1, 2, 3, 4));

    return 0;
}